The present inventors have enthusiastically studied with a principal view toward finding out those useful as agricultural and horticultural fungicides, especially toward developing fungicides capable of exhibiting activities against late blight and downy mildew which result in severe economical damages. Since the pyrimidine ring appeared to play certain special role in interaction with organism, the present inventors have studied in various ways while paying particular attention to pyrimidine derivatives.
A number of researches have hitherto been carried out on pyrimidine derivatives, resulting in the syntheses of a huge number of compounds. Many compounds have been found to have certain characteristic physiological activities in the fields of agricultural chemicals and medical drugs. However, there have still not been known any attempts of actual use of agricultural and horticultural fungicides which contain thiocyanopyrimidine derivatives each obtained by introducing a thiocyano group in the pyrimidine ring. There are very few reports dealing with the syntheses of pyrimidine derivatives containing thiocyano groups. Their biological activities are scarcely known too. They are known only to such an extent that certain thiocyanopyrimidine derivatives and their in-vitro antimicrobial activities are described in Yakugaku Zasshi, 83, 1086 (1963). In this literature, fifteen thiocyanopyrimidine derivatives and their antimicrobial activities are described. It is described that 2-(or 6 -)chloro-4-methyl-6-(or 2-)thiocyanopyrimidine (hereinafter it is referred as 2-chloro-4-methyl-6-thiocyanopyrimidine) is the most active compound and the antimicrobial activities of those having substituent groups at the 5th position of the pyrimidine ring tended generally to be low. Amoung the fifteen compounds described in the above literature, it is only the above-given compound that contains a halogen atom, to say nothing of thiocyanopyrimidine derivatives containing two halogen atoms.
The present inventors carried out an investigation on thiocyanopyrimidine derivatives each of which contained two halogen atoms and in addition, an alkylthio group at the 5th position. As a result, it has surprisingly be found that these derivatives have excellent activities against numerous plant pathogens led by late blight and downy mildew and their activities can be significantly enhanced by introducing alkylthio groups to their 5th positions.